Modern society has imposed numerous requirements for filtering contaminants and undesirable constituents from air and gas flows. Environmental concerns and regulations demand that most business and industrial concerns clean any discharged air before the air passes into the ambient environment. One particularly challenging example is the requirement to filter high concentrations of smoke and fat airborne contaminants from the cooking exhaust of restaurants and food preparation facilities. Burning fossil fuels in the generation of electrical power is another, large-scale example. A variety of different filters and cleaning devices have been developed for addressing some of these needs and requirements.
Static high efficiency particle (HEPA) filters are commonly used for relatively small volume cleaning and filtering applications. In conditions with very high contaminant concentrations in the air or in very high flow volume situations, however, HEPA filters are not practical, because HEPA filters will become clogged with particles too rapidly and have to be replaced or serviced too often. HEPA filters are also very expensive.
Scrubbers are a well-known type of cleaning apparatus. Contaminated air or gas passes through a water mist curtain, a waterfall-like flow of water or cleaning liquid, packed beads or electrostatic precipitators and some of the airborne contaminants become entrained in the water or cleaning liquid, or on beads or charged plates of the precipitators, while the partially cleaned air or gas passes from the device. The accumulated contaminants are flushed out periodically, and the scrubber is otherwise cleaned out, typically with hot water and detergent, achieving a level of self-cleaning functionality. Since the contaminants are removed by the cleaning fluid or water and continually washed away, there are no filters or other similar components which need to be replaced or serviced on a periodic basis. Scrubbers are usually preferred for high volume and heavy contamination applications because of their ability to operate continuously without intense maintenance. Scrubbers have also been used as a pre-filter for removing contaminants from an airflow prior to fine-filtering by one or more HEPA filters.
In general, scrubbers have not been fully successful in removing a sufficiently large percentage of airborne contaminants to be practical in certain high contaminant concentration or high volume airflow situations. For example, water scrubbers that have been used to clean the cooking exhaust of a restaurant or the coal dust in the air of a coal mine have had to rely on HEPA or other filters for their primary air cleaning due to the low efficiency of cleaning from the water scrubbing effect. Another difficulty with water or liquid scrubbers is that they introduce relatively large quantities of water or other cleaning liquid into the exiting air or gas flow. Such scrubbers often require a separate filtering or screening section simply to remove the excess moisture or cleaning fluid before it is discharged into the environment. Additionally, electrostatic precipitators can cause fires or explosions.
It is with respect to these and other considerations, that the present invention has evolved.